Susceptors have been used in conventional microwave heating packages to enhance the heating, browning, and/or crisping of food items. A susceptor generally comprises a thin layer of microwave energy interactive material (generally less than about 100 angstroms in thickness, for example, from about 60 to about 100 angstroms in thickness, and having an optical density of from about 0.15 to about 0.35, for example, about 0.21 to about 0.28) that tends to absorb at least a portion of impinging microwave energy and convert it to thermal energy (i.e., heat) at the interface with the food item. Susceptors are typically supported on a microwave energy transparent substrate, for example, a polymer film, thereby collectively forming a “susceptor film”. Susceptor films, in turn, are often joined to a dimensionally stable supporting material (or “support”), for example, paper or paperboard (“moisture-containing supports” or “fiber-based supports”), to collectively define a “supported susceptor film”.
Supported susceptor films may be used alone or in combination with numerous other materials to form various microwave heating constructs. However, when the exposed side of the moisture-containing support is joined to another layer using a continuous layer of adhesive, the resulting structure may tend to delaminate during heating. While not wishing to be bound by theory, it is believed that during heating, the moisture in the moisture-containing support is released as water vapor, which exerts a pressure on the adjacent layers of the structure. With no path for the water vapor to escape, the layers of the structure tend to delaminate and loft away from one another. In some cases, this lofting or pillowing of the structure can cause the food item seated on the structure to be turned over or toppled undesirably. This phenomenon has been observed both when the supported susceptor film has been joined to another fiber-based layer and when the supported susceptor film has been joined to another polymer film layer.
It is known that structures with more than one susceptor may generate more heat than structures with a single susceptor. Thus, in such multi-susceptor structures, the risk of delamination may be amplified. For example, where a structure comprises a pair of susceptor films joined to opposite sides of a support layer (e.g., paper or paperboard) using continuous layers of adhesive (as is needed to stabilize the susceptor film), the structure may tend to delaminate or rupture upon heating. Thus, there remains a need for a multi-susceptor structure that resists unintentional, uncontrolled delamination during use. There also remains a need for a method of making such a structure.